Combustor heat shield

ABSTRACT

A gas turbine engine combustor has a dome and a shell extending axially from the dome. The dome and the shell cooperates to define a combustion chamber. A dome heat shield is mounted to the dome inside the combustion chamber. A front heat shield is mounted to the shell inside the combustion chamber. The dome heat shield and the front heat shield have axially overlapping portions cooperating to define a flow guiding channel. The flow guiding channel has a length (L) and a height (h). The length (L) is at least equal to the height (h).

TECHNICAL FIELD

The application relates generally to gas turbine engines and, moreparticularly, to combustor heat shields.

BACKGROUND OF THE ART

Heat shields such as those used to protect the combustor shells, areexposed to hot gases in the primary combustion zone. The amount ofcoolant available for cooling the heat shields must be minimized toimprove the combustion efficiency and to reduce smoke, unburnedhydrocarbon and CO/NOx emission.

There is a continuing need for improved heat shields and targetedcooling schemes.

SUMMARY

In one aspect, there is provided a gas turbine engine combustorcomprising: a dome, a shell extending axially from the dome, the domeand the shell cooperating to define a combustion chamber, a dome heatshield mounted to the dome inside the combustion chamber, a front heatshield mounted to the shell inside the combustion chamber, the dome heatshield and the front heat shield having axially overlapping portionscooperating to define a flow guiding channel, the flow guiding channelhaving a length (L) and a height (h), the length (L) being at leastequal to the height (h).

In a second aspect, there is provided a gas turbine engine combustorhaving an annular dome; inner and outer shells extending generallyaxially from the annular dome, the annular dome and the inner and outershells defining a combustion chamber; a dome heat shield mounted to theannular dome inside the combustion chamber, the dome heat shield havinga back face facing the annular dome and an opposed front face facing thecombustion chamber, the dome heat shield further having radially innerand radially outer periphery rails projecting from the back facethereof, the radially inner and outer periphery rails extendingrespectively along radially inner and outer edges of the dome heatshield; and inner and outer front heat shields respectively mounted tothe inner and outer shells, the inner and outer front heat shieldshaving respective upstream end portions extending in overlappingrelationship with the radially inner and outer periphery rails of thedome heat shield so as to define an inner flow guiding channel and anouter flow guiding channel in a region upstream from the front face ofthe dome heat shield relative to a flow of gases through the combustionchamber.

In a third aspect there is provided a method of forming a flow guidingchannel between a dome heat shield adapted to be mounted to a dome of agas turbine engine combustor and a front heat shield adapted to bemounted to a shell of the gas turbine engine combustor adjacent to thedome heat shield, the method comprising: positioning the front heatshield so that an upstream end portion thereof axially overlaps anadjacent peripheral surface of the dome heat shield, the adjacentperipheral surface extending rearwardly from a front gas-path face ofthe dome heat shield and being radially spaced from the upstream endportion of the front heat shield to form therewith a flow guidingchannel in a region of the combustor upstream of the front gas-path faceof the dome heat shield, the relative positioning of the front heatshield and the dome heat shield being selected so that a length (L) ofthe flow guiding channel be equal to or greater than a height (h) of thechannel.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a schematic, cross-sectional view of a turbofan engine havinga straight flow annular combustor;

FIG. 2 is an isometric view of an inlet end portion of the combustor ofthe engine shown in FIG. 1;

FIG. 3 is an enlarged, fragmentary cross-section view of the inlet endportion of the combustor shown in FIG. 2 and illustrating an outer flowguiding channel between a dome heat shield and a radially outer frontheat shield;

FIG. 4 is an enlarged, fragmentary cross-section view of the inlet endportion of the combustor shown in FIG. 2 and illustrating an inner flowguiding channel between a dome heat shield and a radially inner frontheat shield; and

FIG. 5 is an isometric back view of an example of a combustor dome heatshield.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases.

The combustor 16 is housed in a plenum supplied with compressed air fromcompressor 14. As shown in FIG. 2, the combustor 16 comprises an annularcombustor shell 20 including a radially inner shell 20 a and a radiallyouter shell 20 b, defining a combustion chamber 22 therebetween. Theradially inner and outer shells 20 a, 20 b have radially extending endportions which radially overlap to form an inlet dome 24 at an upstreamend of the combustor 16. As shown in FIG. 1, a plurality of fuel nozzles26 are mounted to extend through the dome 24 of the combustor 20 todeliver a fuel-air mixture to the combustion chamber 22.

The radially inner and outer shells 20 a, 20 b extend generally axiallydownstream from the dome 24 to an exit portion or outlet (not shown)formed at a downstream end of the combustor 16 for communicatingcombustion gases to the turbine section 18.

A plurality of impingement holes 28 (FIGS. 2-4) may be defined in theradial and axial portions of the inner and outer shells 20 a and 20 bfor cooling purposes, and dilution holes 29 (FIG. 2) may also beprovided in the axial portion downstream of the fuel nozzles 26 forcombustion purposes. It is understood that the inner and outer shells 20a and 20 b may have any suitable configuration. The inner and outershells 20 a and 20 b are typically made out of sheet metal, though anysuitable material(s) and manufacturing method(s) may be used.

Referring to FIG. 2, it can be appreciated that circumferentiallydistributed dome heat shields 30 (only two being partly shown in FIG. 2)are mounted to the dome 24, inside the combustion chamber 22, to protectthe dome 24 from the high temperatures in the combustion chamber 22.Likewise, circumferentially distributed radially inner and outer frontheat shields 32 a, 32 b are respectively mounted to the axial portion ofthe inner and outer shells 20 a, 20 b immediately downstream from thedome 24. The dome heat shields 30 and the front heat shields 32 a, 32 bare typically castings made out of high temperature capable materials.Each heat shield has a heat shield body typically provided in the formof a circular sector. As shown in FIG. 2, a plurality of threaded studs34 extends from a back face of the heat shield bodies and throughcorresponding mounting holes (not shown) defined in the inner and outershells 20 a, 20 b. Self-locking nuts 36 are threadably engaged on thestuds 34 from outside of the combustion chamber 22 for holding the heatshields 30, 32 a, 32 b tightly against the combustor shell 20.

Referring to FIGS. 2-4, the back face of each heat shield (i.e. the sidefacing the combustor shell) is the cool side of the heat shield, whilethe opposed front face is the hot or gas-path side, facing thecombustion chamber 22. The heat shields 30, 32 a, 32 b are coated ontheir front face. The coating is typically a thermal barrier coating 37(FIGS. 3 and 4). The heat shields 30, 32 a and 32 b are spaced from thecombustor shell 20 so that the back face defines a cooling air space orgap G. As can be appreciated from FIGS. 2-4, rails extend from the backface of each heat shield body across the cooling air gap and intosealing engagement with the combustor shell 20, therebycompartmentalizing the cooling air gap G and directing the cooling airas suited towards targeted areas. More particularly, referringconcurrently to FIGS. 2 to 5, each dome heat shield 30 may be providedwith periphery rails 40 a, 40 b, 40 c and 40 d along the radially innerand outer edges as well as along the opposed side edges thereof, theperiphery rails defining a closed perimeter at the back of the dome heatshield 30. The front inner and outer heat shield 32 a, 32 b may also beprovided with periphery rails 42 at the upstream and downstream endsthereof. Nozzle opening bosses 43 may also project from the back face 30b of the dome heat shields 30 around each fuel nozzle opening 47 (FIG.5) for sealing engagement with an adjacent part of the combustor, suchas a swirler 45 (FIGS. 3 and 4).

In practice, the contact between the periphery rails 40, 42 of the heatshields 30, 32 a, 32 b and the combustor shell 20 is not perfect andcoolant in gap G can leak across the top of the periphery rails 40, 42as schematically depicted by arrows A in FIGS. 3 and 4. It is hereinsuggested to use this periphery rail leakage to form a starter film overthe hot front face of the inner and outer front heat shields 32 a, 32 b.The starter film S helps cooling the inner and outer front heat shields32 a, 32 b. Since the starter film S is spent flow from the dome heatshield 30 and the front heat shields 32 a, 32 b, there is no additionalcompromise to the engine.

Applicant has found that the quality of the starter film S can beimproved by properly guiding the incoming flow of spent coolant over thefront face of the inner and outer front heat shields 32 a, 32 b. In thatregard, it is herein proposed to form flow guiding channels 50 a and 50b between the dome heat shields 30 and the inner and outer front heatshields 32 a and 32 b, respectively. Indeed, the channels 50 a and 50 bmay help reducing the magnitude of the coolant flow disturbances and,thus, provide for a better starter film quality. The length L, L′ of thechannels 50 a and 50 b in a generally axial direction should begenerally greater than their height h, h′ in a generally radialdirection. In other words, the ratios L/h and L′/h′ of channels 50 a, 50b should be equal to or greater than 1.

As shown in FIG. 3 with respect to radially outer channel 50 b, this maybe achieved by increasing the length of an upstream end portion or lip54 b of the outer front heat shields 32 b in the upstream direction soas to axially overlap the radially outer periphery rail 40 b of thecombustor dome heat shields 30. Likewise, the length of the upstream endportion 54 a of the inner front heat shields 32 a may be increased orpositioned to axially overlap the radially inner periphery rail 40 a ofthe combustor dome heat shields 30, as shown in FIG. 4. As shown inFIGS. 3 and 4, the length L and L′ of the inner and outer channels 50 a,50 b may be completed by an axially forward overlap between the innerand outer front heat shields 32 a, 32 b and inner and outer lips 56 a,56 b projecting forwardly from the front face 30 a of the dome heatshields 30 along the radially inner and outer edges thereof in alignmentwith the inner and outer periphery rails 40 a, 40 b. However, the lengtht and t′ of the inner and outer lips 56 a, 56 b (the distance by whichthe lips protrude from the front face of the heat shields into thecombustion chamber 22) of the combustor dome heat shields 30 should beminimized to avoid overheating problems. Indeed, if the dome heat shieldlips 56 a, 56 b extend too far into the combustion chamber 22, they willbe exposed to very high temperatures and, thus, they may eventuallyoverheat and burn out. That is the durability of the lips is better ifthe lips are shorter. Forming a major portion of the channels 50 a, 50 bin an upstream region behind the front face 30 a of the dome heatshields 30 allows to reduce the distance by which the lips 56 a, 56 bmust protrude into the combustion chamber 22 and, thus, reduce thelikelihood of lip overheating problems while still providing asufficient flow guiding length L, L′ for ensuring the quality of thestarter film S. It can be appreciated from FIGS. 3 and 4 that a majorportion of the length L, L′ of channels 50 a, 50 b is disposed upstreamof the front face 30 a of the dome heat shields 30 (i.e. a major portionof the channel length L, L′ is formed between the inner and outerperiphery rails 40 a, 40 b of the dome heat shields 30 and the upstreamlips 54 a, 54 b of the inner and outer front heat shields 32 a, 32 b).

It can also be appreciated from FIG. 3 that the radially outer lip 56 band the radially outer periphery rail 40 b of the dome heat shields 30form a smooth and axially continuous flow guiding surface. Likewise, theradially inner lip 56 a and the radially inner periphery rail 40 a ofthe dome heat shields 30 form a smooth and axially continuous flowguiding surface, as shown in FIG. 4. These inner and outer flow guidingsurfaces are respectively generally parallel to the hot front surface orgas-path side surface of the radially inner and outer front heat shields32 a, 32 b.

As shown in FIGS. 3 to 5, periphery rail holes 60 may be defined alongthe radially inner and outer periphery rails 40 a, 40 b of the dome heatshields 30. The periphery rail holes 60 extend through the rails 40 a,40 b at the root or base of the inner and outer lips 56 a, 56 b, therebyallowing the lips 56 a, 56 b to be cooled by convection. The peripheryair holes 60 have an inlet end which is in fluid flow communication withthe cooling air gap G behind the dome heat shields 30 and an opposedoutlet end which opens into respective channels 50 a, 50 b. Accordingly,a portion of the cooling air or coolant in the gap G behind the domeheat shields 30 will flow through the periphery rail holes 60 into thechannels 50 a, 50 b to combine with the periphery rail leakage A to formthe starter film S over the front heat shields 32 a, 32 b . As can beappreciated from FIGS. 3 and 4, the periphery rail holes may be laserdrilled or otherwise formed at an angle so as to have axial and radialcomponents. The holes 60 are angled so as to have a forward axialcomponent to provide better cooling of the forwardly projectingcombustor dome heat shield lips 56 a, 56 b.

In operation, cooling air in the plenum surrounding the combustor 16will flow through impingement holes 28 defined in the inner and outershells 20 a, 20 b and impinge against the back face of the dome heatshields 30 and the front heat shields 32 a, 32 b. After impinging uponthe heat shields, a first portion of the cooling air will flow througheffusion holes (not shown) defined through the heat shields 30, 32 a, 32b. A second portion of the spent air will leak over the periphery rails40 a, 40 b and 42 into the inner and outer flow guiding channels 50 a,50 b. The remainder of the coolant will flow through the periphery railholes 60 to cool down the heat shield lips 56 a, 56 b. The air flowingthrough the periphery air holes 60 will combine with the periphery railleakage A to form a starter film on the front or upstream portion of theinner and outer front heat shields 32 a, 32 b. The combined flow ofperiphery rail leakage and periphery rail hole flow is guided along thechannels 50 a, 50 b, thereby minimizing flow disturbances and, thus,providing for the formation of a good quality starter film S.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the invention can be provided in any suitable heat shieldconfiguration and in any suitable combustor configuration, and is notlimited to application in turbofan engines. Still other modificationswhich fall within the scope of the present invention will be apparent tothose skilled in the art, in light of a review of this disclosure, andsuch modifications are intended to fall within the appended claims.

What is claim is:
 1. A gas turbine engine combustor comprising: a dome,a shell extending axially from the dome, the dome and the shellcooperating to define a combustion chamber, a dome heat shield mountedto the dome inside the combustion chamber, a front heat shield mountedto the shell inside the combustion chamber, the dome heat shield and thefront heat shield having axially overlapping portions cooperating todefine a flow guiding channel, the flow guiding channel having a length(L) and a height (h), the length (L) being at least equal to the height(h).
 2. The combustor defined in claim 1, wherein a major portion of thelength (L) of the flow guiding channel is located upstream of a frontface of the dome heat shield relative to a flow of gases through thecombustion chamber.
 3. The combustor defined in claim 2, wherein a majorportion of the length (L) is provided at least in part by an upstreamend portion of the front heat shield extending in overlappingrelationship with a dome heat shield periphery rail projecting from aback face of the dome heat shield along an edge thereof adjacent to thefront heat shield, the back face facing the dome.
 4. The combustordefined in claim 3, wherein the axially overlapping portions furthercomprise a lip extending from the front face of the dome heat shieldalong the dome heat shield periphery rail, the dome heat shieldperiphery rail and the lip forming a continuous flow guiding surface. 5.The combustor defined in claim 4, wherein periphery rail holes aredefined in the dome heat shield periphery rail, the periphery rail holesbeing in fluid flow communication with the flow guiding channel and acooling air gap defined between the dome and the dome heat shield. 6.The combustor defined in claim 4, wherein the continuous flow guidingsurface is generally parallel to an opposed gas-path front facingsurface of the front heat shield.
 7. A gas turbine engine combustorhaving an annular dome; inner and outer shells extending generallyaxially from the annular dome, the annular dome and the inner and outershells defining a combustion chamber; a dome heat shield mounted to theannular dome inside the combustion chamber, the dome heat shield havinga back face facing the annular dome and an opposed front face facing thecombustion chamber, the dome heat shield further having radially innerand radially outer periphery rails projecting from the back facethereof, the radially inner and outer periphery rails extendingrespectively along radially inner and outer edges of the dome heatshield; and inner and outer front heat shields respectively mounted tothe inner and outer shells, the inner and outer front heat shieldshaving respective upstream end portions extending in overlappingrelationship with the radially inner and outer periphery rails of thedome heat shield so as to define an inner flow guiding channel and anouter flow guiding channel in a region upstream from the front face ofthe dome heat shield relative to a flow of gases through the combustionchamber.
 8. The combustor defined in claim 7, wherein the inner andouter flow guiding channels have a length (L) and a height (h), andwherein the ratio L/h≧1.
 9. The combustor defined in claim 8, whereinradially inner and outer lips project from the front face of the domeheat shield respectively in alignment with the inner and outer peripheryrails, thereby axially extending the inner and outer flow guidingchannels to a region downstream from the front face of the dome heatshield.
 10. The combustor defined in claim 9, wherein a major portion ofthe length (L) of the inner and outer flow guiding channels is disposeddownstream from the front face of the dome heat shield.
 11. Thecombustor defined in claim 9, wherein the inner and outer lips have alength (t), the length (t) being smaller than a length of the overlapbetween the upstream end portions of the inner and outer front heatshields and the inner and outer periphery rails of the dome heat shield.12. The combustor defined in claim 9, wherein the radially inner andouter lips respectively define with the inner and outer periphery railscontinuous inner and outer surfaces.
 13. The combustor defined in claim9, wherein periphery rail holes are defined in the inner and outerperiphery rails, the periphery rail holes being in fluid flowcommunication with the inner and outer flow guiding channels and with acooling air gap defined between the dome heat shield and the annulardome.
 14. A method of forming a flow guiding channel between a dome heatshield adapted to be mounted to a dome of a gas turbine engine combustorand a front heat shield adapted to be mounted to a shell of the gasturbine engine combustor adjacent to the dome heat shield, the methodcomprising: positioning the front heat shield so that an upstream endportion thereof axially overlaps an adjacent peripheral surface of thedome heat shield, the adjacent peripheral surface extending rearwardlyfrom a front gas-path face of the dome heat shield and being radiallyspaced from the upstream end portion of the front heat shield to formtherewith a flow guiding channel in a region of the combustor upstreamof the front gas-path face of the dome heat shield, the relativepositioning of the front heat shield and the dome heat shield beingselected so that a length (L) of the flow guiding channel be equal to orgreater than a height (h) of the channel.
 15. The method of claim 14,wherein the adjacent peripheral surface of the dome heat shieldcomprises a periphery rail projecting from a back face of the dome heatshield.
 16. The method of claim 15, further comprising providing a lipon the front gas-path face of the dome heat shield in continuity to theperiphery rail.
 17. The method of claim 16, wherein the lip overlaps thefront heat shield along a length (t), the length (t) is less than alength of the overlap between the front heat shield and the adjacentperipheral surface extending rearwardly from the front gas-path face ofthe dome heat shield.